> The obvious counterexample is NOBUS[0] vulnerabilities, and intentional backdoors like the Clipper Chip[1] or Dual_EC_DRBG[2]: if you genuinely believe you are the only one who could possibly exploit it, there's no reason to avoid using it.

The problem with these examples is that they weren't used in national security systems, which are the systems for which NSA has a legislated defensive responsibility.

Clipper was designed for use by the public; it was not intended to ever be used to protect classified (or even sensitive unclassified) information at all.

Likewise with Dual_EC_DRBG. The CSfC component requirements drew from the Common Criteria Protection Profiles, where Dual_EC_DRBG was never an option.